In recent years, a content exchange system that while a user provides another user with a content such as music data owned by the user via the Internet through the use of a PC (Personal Computer), another user provides the user with a content not owned by the user has been developed.
In the system of this kind, theory holds that if one content exists, all other users can use the content, thereby a large number of users will not purchase the content. As a result, the content as a copyright work does not sell well, so the copyright holder of the content will lose an opportunity to receive a royalty that the copyright holder is supposed to receive every time the content is sold. Therefore, it is socially required to prevent unauthorized copying and use of contents which are not licensed by copyright holders without interfering with the distribution of the contents.
In order to respond such a requirement, for example, as described in Japanese Unexamined Patent Application Publication No. 2002-359616, a technique called OpenMG X (trademark) that while contents can be freely distributed, the contents can be used by only authorized users has been proposed.
The technique is as described below. A client receives an encrypted content from a content server. In the header of the content, license identification information for identifying a license required to use the content is included. The client requests the license from the license server on the basis of the license identification information. When the license server receives the request for the license, the license server executes a charging process, then submits the appropriate license to the client. The client can decode and replay the content on condition that the client holds the license. In the technique, while the contents can be freely distributed, only authorized users can use the contents, so while preventing the unauthorized use of contents, the distribution of contents can be promoted.
According to explosive diffusion of the Internet and rapid deployment of broadband technologies in recent years, it is expected that not only PCs but also electronic devices for consumer electronics called CE (Consumer Electronics) devices will be directly connected to a network. Moreover, it is expected that one user will own a plurality of PCs or CE devices capable of accessing the Internet.
However, when a plurality of devices owned by an individual are connected to a network, a conventional model that contents or licenses are controlled by only one device which downloads the contents or the licenses is not user-friendly. For example, in the case where a user uses his home PC to purchase a content through a network, even if the user wants to use the content in a portable device outside the house, he has no choice but to purchase the content again.